CMake building a static library with other static library

Question

My problem is as follows :

I have OpenSSL as static libraries (libcrypto.a and libssl.a). Compiled on Windows with MSys2/MinGW64. Besides that, I have a small self written library based on OpenSSL.

Now I want to "bundle" the Crypto lib from OpenSSL with My lib to a "big" static library for later statically compiling in other applications on Windows without deploying any library.

What would a CMakeLists.txt file looks like? And are the prerequisites (OpenSSL as static libs) correct?

Actually compiling this to a dynamic DLL works like a charm. But My static lib are only includes the symbols of My own library, not from OpenSSL too.

Actually I have no working CMake file, so I can't include an example. I'm just looking for a direction how to do it.

A short suggestion how to begin would be highly appreciated.

In short, CMake [doesn't help](https://cmake.org/pipermail/cmake/2010-April/036669.html) you in combining several static libraries into single one. You may use `add_custom_command`/`add_custom_target` for specify utilities invocation, which does that job. CMake-**unrelated** ways see in that question: https://stackoverflow.com/questions/3821916/how-to-merge-two-ar-static-libraries-into-one. — Tsyvarev, Apr 20 '18 at 17:27

score 2 · Accepted Answer · answered Apr 20 '18 at 17:21

If what you really want to do is combine multiple static libraries into one, for the convenience of external consumers, you'll probably need to run a custom command to do this (as it's not something that's frequently done).

Using the GNU toolchain, the commands to do so might look something like this (untested though):

${CMAKE_COMMAND} -E make_directory tempdir
cd tempdir
${CMAKE_AR} x $<yourlib:TARGET_FILE>
${CMAKE_AR} x ${OPENSSL_CRYPTO_LIBRARY}
${CMAKE_AR} x ${OPENSSL_SSL_LIBRARY}
${CMAKE_AR} cf ${CMAKE_BINARY_DIR}/bin/libyourmegalib.a *.o
cd ..
${CMAKE_COMMAND} -E remove_directory tempdir

Then you would use add_custom_command() to create a target to run this script - either put those lines as COMMAND arguments, or create a script template, substitute values at CMake generation time using configure_file(), then have the custom command run that script.

That said, if the external consumers are all using CMake themselves, I would skip this entirely, and just have the installation process for your library generate CMake package configuration files that declare the dependencies on the OpenSSL libraries.

Thanks alot, now CMake becomes more clear. That was exactly what I needed. — Eurobertics, Apr 23 '18 at 09:36

score -1 · Answer 2 · answered Apr 20 '18 at 16:10

-1

target_link_library() works both for add_executable() and add_library(), so you should be able to do:

add_library(yourlib STATIC ...)
target_link_libraries(yourlib lib1 lib2 ...)

(where yourlib is your library, and lib1, ... are the libraries you want to bundle.

answered Apr 20 '18 at 16:10

Marco Pantaleoni

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`target_link_libraries` doesn't **bundle** other libs into your one. So, when create an application which uses `yourlib`, it still requires `lib1`, `lib2` libraries to be existed. – Tsyvarev Apr 20 '18 at 17:31

CMake building a static library with other static library

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